1. Field of the Invention
The present invention relates to a semiconductor device which includes therein a device (hereinafter referred to as a light emitting device) having an element where a light emitting material is sandwiched between electrodes (hereinafter referred to as a light emitting element) or a device (hereinafter referred to as a liquid crystal display device or a liquid crystal module) having an element where liquid crystal is sandwiched between electrodes (hereinafter referred to as a liquid crystal element), and a method of manufacturing thereof. For example, the present invention relates to an electric device represented by a liquid crystal display device and a light emitting device, and to an electronic equipment (electronic apparatus) having such an electric device (electronic device) mounted thereon as a component.
It is to be noted that, as used herein, the term “semiconductor device” refers to any device which can function by utilizing semiconductive characteristics, including an electric device, a semiconductor circuit, and an electronic apparatus.
2. Description of the Related Art
These days, attention is attracted to technology for forming a thin film transistor (hereinafter referred to as a TFT) using a semiconductor thin film (at the thickness of several to several hundred nm) formed on a substrate having an insulating surface. A thin film transistor is widely applied to electronic devices such as an IC and an electric device. In particular, a thin film transistor as a switching element in a liquid crystal display device and in a light emitting device is actively developed for practical use.
Also, recent trend toward lighter devices in weight has induced attempt to form a light emitting element or a TFT on a flexible plastic film. However, the present situation is that a satisfactory TFT compared with one formed on a glass substrate has not been manufactured as yet.
Development of a light emitting device (also called a light emitting diode or an electroluminescent (EL) device, and hereinafter referred to as an EL display device or an EL module) using a light emitting element (hereinafter referred to as an EL element) utilizing an electroluminescent light emitting material (hereinafter referred to as an EL material) is making progress. An EL display device is structured to comprise an EL element where an EL material is sandwiched between an anode and a cathode. By applying voltage between the anode and the cathode, electric current is made to pass through the EL material, carriers are made to recombine, and light is emitted. Since, in this way, a light emitting element itself has the ability of emitting light in an EL display device, a backlight which is used in a liquid crystal display device is unnecessary. In addition, an EL display device has a wide angle of visibility, is light in weight, and has low power consumption.
To make the EL display device capable of displaying colors, there are methods: a method where EL elements emitting red, green, and blue colors are arranged in a matrix; and a method where EL elements emitting white light are used together with color filters.
In an EL display device where EL elements emitting red, green, and blue colors are used, since different EL materials are used to form EL elements emitting the respective colors, the element characteristics differ accordingly, and it is difficult to obtain uniform display.
In a color EL display device where EL elements emitting white light are used together with color filters, R (red), G (green), and B (blue) color filters are formed at positions corresponding to pixels, thereby changing colors of light to be taken out from the respective pixels. It is to be noted that, positions corresponding to pixels mean positions aligned with pixel electrodes. The color filters have an R (red), G (green), or B (blue) coloring layer, and a color shielding mask provided, except at positions corresponding to gaps of pixels. By making light transmit the color filters, red, green, and blue light are extracted. The light shielding mask of the color filters generally comprises a metal film or an organic film containing black pigment.
In a liquid crystal display device, TFTs using semiconductor of amorphous silicon or polysilicon are arranged in a matrix. A liquid crystal material is sandwiched between an element substrate where pixel electrodes, source lines, and gate lines connected to the respective TFTs are formed, and an opposing substrate having an opposing electrode disposed so as to face the element substrate. Color filters for color display is formed on the opposing substrate. In principle, such a liquid crystal display device is similar to that of the EL display device using the color filters as described above. Further, a polarizing plate is disposed as a light shutter on each of the element substrate and the opposing element to display a color image.
Also, a liquid crystal device using a metal film as the light shielding mask has a problem that signal delays are liable to occur due to parasitic capacitance formed between the metal film and other wirings. A liquid crystal device using an organic film to insulate the light shielding mask from other wirings has a problem that the number of the manufacturing processes increases.